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Old 29th December 2002, 03:33 PM   #1
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Question electrical or cone damping

All you out there:

In order do damp a vented box more, you can either (or both) increase electrical or cone damping. Electrical damping can be increased by negative output resistance on amplifier. Cone-damping can be increased by adding acoustic material to the speaker basket.

Which is the best ?
Adv.
Electrical damping
Adv.
Higher sensitivity on speaker
Disadv.
Amp oscillations ?
Difficult ?
Higher displacem on speaker

Cone-damping
Adv
Lower displacem on speaker
Easy

Any comments ?
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Old 29th December 2002, 04:27 PM   #2
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Putting damping material on the basket of a driver will not damp the cone--only the basket. That's not to say that it's a bad idea to damp any possible resonances in the basket. It's just that they're two different things. You can have low Zout on your amplifier <i>and</i> put damping material on your driver baskets if you want. There's no conflict between the two.
If, perhaps, you meant putting some sort of damping material on the cone, then you're going to change the Thiele-Small parameters of the driver. That will change how the driver relates to the box and give unpredictable response. If you modify a driver in this manner, be prepared to measure the new Thiele-Small parameters and build a new box.
Also, watch out for the suspension on the driver. It may not be able to take much added mass and you could end up rubbing the voice coil against the magnet structure, which would destroy the driver in short order.

Grey
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Old 29th December 2002, 04:36 PM   #3
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Well GRollins !
Ive not been too accurate..........
The cone-damping method I was thinking of is a relatively old one: Add the acousticly damping material to the basket in a way that basket-holes will be covered which means that sound, created by the cone, will have to pass. At or around fs, damping will be more efficient than higher up since cone-displacement is higher here.
This method was used in the old days when wide-band-speakers had to high Qts to be used in other boxes than sealed ones, TQWTs or horns. The actual goal was to reduce cone-displacement.
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Old 2nd January 2003, 01:44 PM   #4
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and the result will be a dull sound. Seriously, inhibiting the air flow around the chassis is one of the worst things to do. The damping is highly nonlinear as a function of excursion, air speed and frequency, and there will be some time smear because air flows/eddies need some time to stop again.

This is why most modern designs have vented spiders, magnets etc.
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Old 2nd January 2003, 01:58 PM   #5
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Thanks Capslock !

So the best way to add damping should be to use negative out-put impedance at power-amplifier, right ?
Unfortunatly, this will cause a slight rise in cone-movement...

Most woofers do reproduce high-bass a bit "bumpy" due to floor/wall reflections. The added damping is requested to make high-bass sound more accurate/rigid/dry.

Have you got any suggestions regarding good woofers for use in small vented boxes like 20 liters ?

Many Scan-speak will do and some VIFA or Seas too. JBL of course but then youve got the price on them........Im aiming at a stock-price of $50-60 each.

Happy New Year !

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Old 2nd January 2003, 04:13 PM   #6
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Bjed,

With such a small box, why not just go with a closed box system. Youll get the damping inherent in the alignment, you wont need to play with negative feedback that will affect the amp operation and sound, you dont have to worry about cone excursion below f3, and youll have better transient performance. If you need more bass extension, you can add an electronic bass boost circuit or use the room gain (I would prefer the former) without affecting the amp or driver parameters.

Just a thought,
Rodd Yamashita
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Old 2nd January 2003, 04:48 PM   #7
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Hi,

Use of negative resistance is worse either. You are making the damping highly depending on the voice coil magnet system then and its non-linearity. Note, that the resistance of the voice coil is dependent on its temperature. Using a negative resistance makes the damping even more dependent on voice coil temperature modulation.

I Have good results with taming the Q of a (closed) box by using an electronic bi-quad compensation filter like that of Linktwitz: http://www.linkwitzlab.com/

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Old 2nd January 2003, 04:54 PM   #8
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Hi Pjotr !

You mean, taming Q with "The Linkwitz Transform circuit" ?
Actually lower the boxs total Q ?
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Old 2nd January 2003, 05:07 PM   #9
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Hi bjed,

Yes indeed, but I have no experience with BR boxes. Only with closed boxes.
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Old 2nd January 2003, 05:58 PM   #10
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Default Passive Crossovers kill Dampening

It's been my understanding that the quality of the Amplifier's output stage in conjunction with the driver, and any inserted passive networks is what determines how well the cone tracks the signal, and most high quality Amps and Drivers have very good Dampening characteristics until they are coupled with the passive components in-between.

I may not be entirely correct on my ideas of dampening (mechanical) but I do know from experience and written documentation that the best way to significantly increase mechanical dampening of the drivers is to simply remove or reduce the passive filter components to a minimum. I've never heard any complaints of cone oscillation problems loose or muddy bass on any Actively filtered system, in fact that is the strongest advantage of Active networks IMO, the phenomenal increase in Dampening.

So any method of increasing dampening seems wasted to me when most of all the driver control is being robbed by de-coupling the Amp's outputs to the driver's inputs via passive crossover networks.
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